Enhance the C++ implementation to overload subscripting with operator [I so that fields can be accessed as csv[i].

Enhance the C++ implementation to overload subscripting with operator [I so that fields can be accessed as csv[i].

Enhance the C++ implementation to overload subscripting with operator [I so that fields can be accessed as csv[i].

Enhance the C++ implementation to overload subscripting with operator [I so that fields can be accessed as csv[i].